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Path: utzoo!linus!security!genrad!decvax!decwrl!rhea!castor!covert
From: covert@castor.DEC (John Covert)
Newsgroups: net.dcom
Subject: Cost of X.25 networks vs. cost of 1200 bps
Message-ID: <6482@decwrl.UUCP>
Date: Sun, 25-Mar-84 09:55:45 EST
Article-I.D.: decwrl.6482
Posted: Sun Mar 25 09:55:45 1984
Date-Received: Mon, 26-Mar-84 01:08:43 EST
Organization: DEC Engineering Network
Lines: 27

At 1200 bps, I can transmit (with an error correcting protocol)
approximately 5120 characters per minute, or per 47 cents (the
maximum cost of an interstate telephone call within the continental
U.S.).
 
This is 9.18 cents per kilocharacter.  Unless I'm mistaken, most
X.25 services charge much more than 9.18 cents per kilocharacter.
 
The basic line charge for an X.25 connection is drastically higher
than for a telephone; X.25 rates include both a time and a kilocharacter
component.
 
And note that the throughput I get with my error correcting protocol
is only 683 bps; a better protocol implementation should be able to
get that 56% line utilization up to over 80%.
 
And with a 2400 bps modem my kilocharacters should cost 4.6 cents.
 
Those 9600 bps access lines look real neat, until you find out that
the throughput of most X.25 networks is MUCH less.  I've measured
throughputs as low as 600 bps (gee, right there with my 1200 bps
modem and its error correcting protocol).
 
I'm not sold on the current X.25 offerings.  The potential is there,
but the economics don't justify it yet.
 
John Covert		...{decvax|ucbvax|allegra}!decwrl!rhea!castor!covert